A New Hybrid Submodule for MMC with DC Fault Ride-Through Capability

Modular multilevel converter (MMC) has become the most prominent topology for high voltage direct current. (HVDC) applications due to its modularity, lower losses, less filtering requirements and flexible controllability. However, MMC still lacks in terms of efficiency and fault tolerant capability compared to the line commutated converters (LCC) based HVDC systems. This paper proposes a thyristor bypassed fault tolerant half bridge submodule (TBFT-HBSM) for MMC to achieve high efficiency as that in LCC while retaining DC fault tolerant capability and controllability. The lower switch of conventional HBSMs is replaced by anti-parallel thyristor switches to reduce the overall conduction losses of the converter. A new control algorithm has been proposed to balance the arm voltages. Moreover, loss analysis of proposed submodule (SM) is carried out and its efficiency compared with existing SM topologies. Simulation as well as experimental studies are carried out to verify the effectiveness of the proposed SM structure and its control.